1. Field of the Invention
The present invention relates to a low drop-out voltage regulator and in particular to a low drop-out voltage regulator having a fast response time.
2. Description of the Related Art
Low drop-out (LDO) voltage regulators are used to provide a steady voltage level that is lower than the supply voltage level. Such regulators should be able to provide a steady voltage level at the same time as providing the current to a load.
A P-channel MOS transistor (PMOS) is generally used in LDO voltage regulators as the pass device connected between the supply voltage and the load connected to the output of the LDO circuit. This PMOS is then controlled by control circuitry to perform the role of providing the required voltage level, for whatever current is required by the load.
Depending on the type of load, the current required by the load may vary. A problem occurs in some known LDO circuits when the load current varies rapidly. This is because the PMOS pass device is generally a relatively slow device, having a slow response to changes in the control signal provided at its gate terminal. This slow response results in the output voltage of the LDO circuit fluctuating, which is undesirable as this generates noise, and causes problems at high frequencies.
In order to minimize the voltage fluctuations at the output of known LDO voltage regulators, an output capacitor is often provided. However, the output capacitor is required to be relatively large in order to adequately minimize voltage fluctuations, for example in the range of 0.5 μF to 10 μF depending on the scale of current variations. The necessity to provide such a large capacitor is disadvantageous as an additional discrete component is required that adds to the cost of manufacturing the device.